In rail vehicles, adjacent freight cars which are located together on a truck (for example Jacobs truck) are coupled by means of semi-permanent connections. Said connections are also referred to as “tight couplings.” Vehicles having connections of this type are also referred to as “tight-coupled units.” For the most part, only two vehicles are coupled to each other, but sometimes there are also more.
The object of said tight coupling is to transmit the tensile and compressive forces in the longitudinal direction of the vehicle from one freight car to the other upon acceleration and braking. Furthermore, said tight coupling is intended to transmit the transverse forces during curve travel and due to weight. The coupling is intended to ensure mobility about all three axes in space. During curve travel, the main movement angles occur about the vertical z axis. If depressions or bumps are crossed, tilting angles about a horizontally extending y axis and rolling angles about an x axis extending in the longitudinal direction of the train also occur and should be compensated for by the coupling. Furthermore, a tight coupling should not have any linear degrees of freedom in order to avoid jolting during changes of load.
There is a number of known solutions for the above-mentioned application. Said solutions are based predominantly on the fact that a radial swivel bearing having a horizontal bearing axis forms the central element of the articulated connection. The swivel bearing has the required rotatory angular movements because of suitable geometry in all three pivot axes. For this purpose, the swivel bearing is fixed via the outer ring thereof in a coupling housing. The housing constitutes a swivel head and is suitably connected in the longitudinal direction of the vehicle to the vehicle frame of one of the freight car ends to be connected. A welded joint is usually used for this purpose. The swivel bearing is fixed via the inner ring thereof to a stem or a shaft and the latter is fixed in turn in a housing. In various solutions of the prior art, the stem and inner ring are designed as a single part. The housing in turn is likewise connected in the longitudinal direction of the vehicle to the end of the second freight car to be connected. A welded joint is customarily also used for this. The housing is frequently shaped at the bottom in such a manner that it can be directly supported on the center plate of the truck. The required articulated connection is thereby formed. Said solutions from the prior art have swivel bearings requiring maintenance (lubrication with grease/oil) or swivel bearings which are maintenance-free (sliding layers between the outer and inner rings). Furthermore, solutions requiring maintenance and having other bearing solutions are known, but said solutions do not meet the ever-increasing service life requirements.
However, these known solutions from the prior art all have disadvantages. For example, the coordination of tolerances of the stem, housing, supporting disks and bearing width is difficult with regard to a play-free stem connection. Furthermore, the assembly/removal in the event of deformation of the stem is difficult. The stem seat in the housing or the inner ring seat on the stem frequently becomes corroded. The possibility of maintaining the known tight couplings of this type is therefore inadequate. Furthermore, the stem is insufficiently fixed in the housing. Constructional forms which are not sealed cause a high outlay on maintenance due to the required regreasing.
A further known type of articulated coupling unit for the semi-permanent connection of railroad freight cars is known from DE 691 08 977 T2. However, sealing of the bearing elements is not provided, and this restricts the use. In this coupling unit, the use of a wedge-shaped clamping part in order to fix the receiving stem of the inner bearing part on the housing is disadvantageous with regard to secure fastening and freedom from play, in particular in the event of shaking.